Laser servowriting is used in connection with flexible magnetic data storage disks to increase the storage density of the magnetic media by allowing for more precise positioning of the read/write heads. The increased precision in positioning is provided by using an optical servo system that detects an optical servo pattern formed on or in the surface of the disc. The optical servo pattern can consist of a large number of equally spaced concentric tracks. Each track can be a single continuous groove, a plurality of equally spaced pits, or a plurality of relatively short equally spaced grooves or stitches.
The optical servo pattern is typically formed using light energy, e.g., a laser, that is focused into a spot having the desired width of the tracks to be formed on the disk. The focused spot of laser energy is typically translated across the radius of the media by moving a lens and mirror arrangement located on an optics sled. The optics sled is translated over the desired distance and along the direction of the laser energy, thereby causing the focused spot of laser energy to also move.
Control over movement of the optics sled is an important issue because the location of the focused spot of laser energy is critical in formation of the desired optical patterns. Variations in the size or location of the focused spot can cause corresponding variations in the optical contrast and/or location of the optical patterns. Such variations can be detrimental to the storage of data on the resulting magnetic data storage discs.
Among the causes of variations in the location and/or size of the focused spot size are deviations in the movement and orientation of the optics sled carrying the optics used to both redirect and focus the laser energy. Among those deviations are changes in the pitch and yaw of the optics sled with respect to the media, as well as errors in the location of the optics sled as it translates across the radius of the media.
In addition to deviations such as pitch and yaw, vibrations induced in the optics sled can also cause variations in the optical track pattern. Those vibrations may be caused by the alignment of the actuator or actuators used to move the optics sled. Where the resultant force produced by the actuators is not directed through the center of mass of the optics sled, moments can be induced that can cause the optics sled to vibrate about one or more axes. In some instances, the speed of the laser servowriting process can be limited by those vibrations.
One attempt to reduce vibrations caused by the resultant force includes mounting additional balancing masses on the optics sled in an attempt to move the center of mass of the optics sled. By adjusting the position of the balancing mass or masses, it may be possible to reduce vibration of the optics sled by moving the center of mass into alignment with the resultant force produced by the actuator or actuators. Balancing masses are, however, difficult to adjust initially and may required readjustment after use. In addition, the additional mass can reduce the acceleration of the optics sled, thereby increasing cycle time.